Keep in mind, there are places, here in America and around the world where you do NOT have access or the ability to a water hose and running water to wash a car. Isn't going to happen. So if you want to get your car clean you have to find a different method and at some point, with whatever method you choose, you have to "touch" your car.
The key thens is the thing I'm always harping on is many of my posts and that's understanding how to "touch" your car in a way that you won't scratch it.
In the last two days I've used a waterless wash to was two VERY dirty cars. I didn't want to use a waterless wash one car because it was covered with tree sap mist and pollen, which formed a sticky paste over all the horizontal surfaces.
The way I approached this car was to spray on a LOT of waterless wash, to the point the car had a complete film of liquid on the horizontal surfaces. I did this to all the horizontal surface to the waterless wash could start soaking in, penetrating this sticky film so I could more easily wipe it off.
I had to go over the car a second time to remove the smears from the first wipe-down because it was so gross.
The second car was my truck and it sat outside at the beach for three days and it too was covered with tree sap mist and pollen. I did the same as above, laid down a HEAVY layer or waterless wash and then used multiple towels to wipe the truck clean.
The dirtier the vehicle, the more product you use and the more towels you need to have at the ready.